The explode application has been refactored to be callable and Makefile test...

The explode application has been refactored to be callable and Makefile test converted to a gtest. (#5590)

* Updated explode application gtest to use DefaultCube fixture instead of cube in isis/tests/data. Addresses #5557.

* Cleaned up includes in default explode gtest. Added history entry to explode.xml. Addresses #5557.

* Updating main.cpp and removed Makefile tests for explode conversion to callable app. Addresses #5557.

* Added CHANGELOG entry for conversion of explode app to callable function. Addresses #5557.

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Co-authored-by: Adam Paquette <acpaquette@usgs.gov>